Investments Contractual Maturities of Available-for-Sale Fixed Maturity Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Amortized Cost
Due in one year or less, Amortized Cost	$ 17,204
Due after one year through five years, Amortized Cost	65,134
Due after five years through ten years, Amortized Cost	46,019
Due after ten years, Amortized Cost	125,666
Total fixed maturities, Amortized Cost	514,980	$ 422,255
Estimated Fair Value
Due in one year or less, Estimated Fair Value	17,156
Due after one year through five years, Estimated Fair Value	64,920
Due after five years through ten years, Estimated Fair Value	46,028
Due after ten years, Estimated Fair Value	123,455
Total fixed maturities, Estimated Fair Value	508,011	$ 425,191
Asset-backed securities [Member]
Amortized Cost
Without single maturity date, Amortized Cost	151,526
Estimated Fair Value
Without single maturity date, Estimated Fair Value	150,290
Residential mortgage-backed securities [Member]
Amortized Cost
Without single maturity date, Amortized Cost	109,431
Estimated Fair Value
Without single maturity date, Estimated Fair Value	$ 106,162